The most convenient hydrogen chloride generator is that described
by Sweeney.[1] Concentrated hydrochloric acid is introduced
into concentrated sulfuric acid, by means of a dropping funnel
and a _capillary tube leading to the bottom of the sulfuric
acid container_. It is convenient to use a 3-l. bottle for this
container and a 1-l. funnel to contain the hydrochloric acid.
The gas is dried by passing through a wash-bottle containing
concentrated sulfuric acid. An empty catch-flask should be
connected between the generator and the absorption flask in case
any glycerol tends to suck back at the start of the reaction.
About 6 kg. of concentrated hydrochloric acid and 10 kg.
of concentrated sulfuric acid are required in one run.
The generating flask will have to be recharged every six hours;
it should be half filled with sulfuric acid. Aside from this,
the apparatus needs no attention. The oil bath can be conveniently
heated on an electric hot plate.
The dichlorohydrin boiling over a 7'0 range is sufficiently pure for
most purposes. It contains very little, if any, isomeric dichlorohydrin,
since on oxidation it gives dichloroacetone in good yields.